Glow plug

Abstract

A glow plug 1 includes a sheathed heater 3 and a metallic shell 2 . The sheathed heater 3 is configured such that a resistance wire coil 3 b having a heating coil portion 30 b and an insulating MgO powder 3 d are placed in a sheath 3 a and such that a bar electrode 3 c is inserted into the sheath 3 a . The heating coil portion 30 b is formed of a coil base material 31 b and a coating layer 32 b , which covers the surface of the coil base material 31 b . The coating layer 32 b is formed of Pt, Pd, Rh, or an alloy of two or more of Pt, Pd, and Rh.

What is claimed is:  
     
         1 . A glow plug comprising: 
 a tubular metallic shell;    a sheathed heater being inserted into a tubular hole of the metallic shell with a distal end portion of the sheath projecting outward from the metallic shell,    wherein the sheathed heater comprises    a tubular sheath having a closed distal end,    a resistance wire coil disposed in the sheath and having at least a heating coil portion,    an insulating MgO powder charged in the sheath, and    a bar electrode having one end inserted into a rear end of the sheath in a sealed condition,    wherein the heating coil portion comprises a coil base material and a coating layer, which covers the surface of the coil base material, and the coating layer comprises at least one metal or metal alloy selected from the group consisting of Pt, Pd, Rh and an alloy of two or more of Pt, Pd and Rh.    
     
     
         2 . The glow plug as claimed in  claim 1 , wherein the coil base material of the heating coil portion comprises an Fe—Cr—Al alloy.  
     
     
         3 . The glow plug as claimed in  claim 1 , wherein the coating layer has a thickness of 0.2 μm to 0.5 μm.  
     
     
         4 . The glow plug as claimed in  claim 1 , wherein the coating layer comprises Pt.